1. Field of the Invention
The present invention relates to rotary piston engines, and more particularly to housing structures for rotary piston engines. More specifically, the present invention pertains to housing structures for multiple-rotor type rotary piston engines.
2. Description of the Prior Art
In recent years, there is an increasing trend of providing vehicles with high power engines so that the user's demands are satisfactorily met. In the field of rotary piston engines, two rotor type engines have commonly been used, however, rotary piston engines having three or more rotors are being developed to provide a high output power. One example of such multiple-rotor engine is shown in Japanese patent application No. 58-163171 which has been filed on Sept. 7, 1986 and disclosed for public inspection on Apr. 19, 1986 under the disclosure number 60-69208.
In these multiple-rotor engines, problems are produced in that the eccentric shaft must have three or more eccentric shaft sections. In rotary piston engines, the rotors are formed with internal gears which are in meshing engagements with stationary gears provided on the housings. In case where the eccentric shaft has three or more eccentric shaft portions, the shaft cannot be of a one-piece structure because it will become impossible or very difficult to assemble the stationary gears on the housing. In view of the problems, proposals have been made to divide the eccentric shaft into two pieces and connect them together so that they rotate as a unit. Examples of three rotor engines having such eccentric shafts of two-piece construction are shown by Japanese patent diclosures Nos. 60-69204, 60-69205, 60-69207 and 60-69209. In the engine as disclosed by these patent applications, a first eccentric shaft element is provided with two eccentric shaft sections and a second eccentric shaft element having one eccentric shaft section is fittedto the first element to rotate therewith.
As disclosed by the aforementioned Japanese patent applications, the rotary piston engine of this type includes a casing comprised of a plurality of rotor housings assembled together with an intermediate housing disposed between each two rotor housings and a side housing attached to the outer side surface of the outside rotor housing. Those housings are connected together by a suitable number of tightening bolts which are passed through the entire thickness of the casing. The eccentric shaft is located in the casing so that one end of the second eccentric shaft element is at a logitudinally intermediate portion of the casing. It should be noted, however, that this structure has problems in that the eccentric shaft has a minimum rigidity at the portion where the aforementioned one end of the second eccentric shaft element is located with the result that the casing also has the minimum rigidity at a portion corresponding to the said one end of the second eccentric shaft element. Where the housings in the casing are connected together by connecting bolts which pass through the entire thickness of the casing, the connecting bolts are subjected to a large bending stress at the portions corresonding to the said one end of the second eccentric shaft element and therefore the connections between the housings of the casing may be loosened. Further, this structure is inconvenient to assemble because it is required to locate all housings of the casing in axially aligned positions and insert the connecting bolts into axially aligned bolt holes formed in the housings. In this assembling procedure, difficulties may be encountered in inserting the connecting bolts into the bolt holes unless the housings are exactly aligned positions.